More than 10 million people in the U.S. suffer from movement disorders such as essential tremor, dystonia, and Parkinson's disease. Additionally, over three million people in the U.S. and over 50 million people worldwide suffer from epilepsy. One effective emerging treatment for these diseases is deep brain stimulation (DBS) of the subthalamic nucleus with periodic high-frequency electric pulse trains. DBS therapy has been approved by the U.S. Food and Drug Administration for the treatment of Parkinson's disease, essential tremor, dystonia, and obsessive-compulsive disorder, and is showing signs of promise for the treatment of intractable epilepsy and major depression.
DBS devices apply electrical stimulation to a targeted small region of the brain via an implanted electrode to block corrupted neural signals responsible for disease symptoms. The optimal neural target typically occupies a relatively small volume (several cubic millimeters) deep within the brain, which may be a short distance (2-3 mm) from other structures that could lead to serious side effects if they are damaged, disrupted, or inadvertently stimulated by the electrode in the course of targeting or treatment. The accurate placement of the DBS electrode is critical for achieving an optimal treatment effect from DBS therapy with minimal risk and side effects to the patient in both the long and short term. One factor that may affect the accurate placement of the DBS electrode relates to the shifting of the brain that may occur when the skull is opened after images of the brain have been taken. Another factor that may affect the accurate placement of the DBS electrode relates to image resolution limitations that can include an error range of +/−5 mm. Because anatomical information of the brain attained by computed tomography (CT) and/or magnetic resonance imaging (MRI) devices may be inadequate by itself for defining the best target, functional mapping of the brain is also utilized in DBS surgery.
Functional mapping of the brain involves penetrating computed target structures with a microelectrode to identify the neuronal structural boundaries using electrical activity picked up or received by the tip of the microelectrode. There is sufficient variability among individual functional anatomy and pathological localization to utilize functional (e.g., electrophysiological) information along with anatomical information for target verification in an individual patient. Electrical activity is measured in two main neural potentials: single unit action potentials (SPIKES) and local field potentials (LFP). Neuronal structure boundaries are identified using SPIKES, for example, received by the microelectrode. The measured SPIKES from the microelectrode are analyzed acoustically in real-time by an electrophysiologist to determine if the intended target region has been found. The primary limitation to this standard practice is the subjective identification of the desired target from the brain image. An error in either method may lead to longer surgeries, increased risk to the patient, and if not corrected, a poorly positioned electrode resulting in a negative patient outcome with poor symptom control and potential stimulation side effects.
The technical challenges of targeting electrode placement in the brain are disincentives for general neurosurgeons to perform DBS surgery. Therefore, a clear and unmet need exists to improve the ease and accuracy of DBS surgery, to reduce surgical risk, to increase the speed of DBS procedures, and to allow more general neurosurgeons to perform DBS surgery.